Broken color inheritance for 3MF export

[jdegenstein]

Currently color inheritance seems to not be working in the way intended, this works:

a=Cone(1,0,2).solid()
b=Box(3,3,3).solid()
a.color = Color(0.137, 0.306, 0.439)  # Tealish
b.color = Color(0.980, 0.973, 0.749, 0.25)  # Transparent Goldish 
exporter = Mesher(unit=Unit.CM)
exporter.add_shape([a,b])
exporter.write("ab_dual_color.3mf")

this doesn't:

a=Cone(1,0,2)
b=Box(3,3,3)
...

The resulting 3MF from the 2nd case has no color or transparency applied. I don't know if this is a regression or not, but I believe we tried to avoid this problem before.

[gumyr]

The problem is at the beginning of the Mesher.add_shape method:

        shapes = []
        for input_shape in shape if isinstance(shape, Iterable) else [shape]:
            if isinstance(input_shape, Compound):
                shapes.extend(list(input_shape))
            else:
                shapes.append(input_shape)

where the sub-Shapes are extracted from the Compound (i.e. Cone or Box) but not any color information from the parent Compound object. This Shape extraction section needs to be reworked.